Oxy-steam gasification in biomass-to -biomethane and -hydrogen processes: a thermo-economic assessment

Global decarbonization efforts require upscaling the production of renewable gases, including biomethane and hydrogen, with ambitions targets set by European legislation. Integrated thermochemical processes based on biomass gasification represent a potentially scalable solution for both products but require specific thermo-economic assessments to define their competitiveness. In this work we evaluate the production of biomethane and hydrogen from oxygen-steam gasification at the small-scale (250 kg/h biomass input) in both standalone and Biomass-Power-to-Gas integrated processes, estimating biomethane and hydrogen yields on biomass of 0.34–0.44 Nm3/kg and 0.49–0.94 Nm3/kg (44–84 g/kg), respectively. Process energy balances show HHV efficiencies of 66–65 % and 68–70 % for biomethane and hydrogen, respectively, where additional heat recovery from downstream purification enhances the otherwise similar efficiency of the hydrogen process. The biofuels minimum selling prices are estimated between 131 and 228 €/MWh (1.35 and 2.39 €/Nm3) for biomethane and between 299 and 329 €/MWh (11.76 and 12.93 €/kg) for hydrogen, for the standalone and Biomass-Power-to-Gas options, respectively. This indicates that if electrolysis is sized based on gasification oxygen requirements it does not deliver any cost benefits despite higher yields. Sensitivity analyses indicate a limited effect of a 50 % increase in fixed capital investment in both cases, while variations in biomass and electricity costs within the integrated Power-to-Gas scenarios show a biomethane and hydrogen price under 200 €/MWh only for electricity costs not greater than 200 and 80 €/MWh, respectively. While the economics remain relatively unfavorable, the study provides useful information for future assessments and indicates oxygen-steam gasification as competitive with conventional steam gasification options.